The present invention relates to an oil supply apparatus for a transmission, which supplies the oil to the transmission by an electric oil pump.
A transmission provided in a drive line of a vehicle performs shift change using oil (working fluid). An apparatus for supplying the oil to the transmission is therefore provided. To provide the oil to the transmission, a pump that pressurizes and discharges the oil is required. As the pump, there are a mechanical oil pump and an electric oil pump. The mechanical oil pump is a pump that is driven by an engine, and the electric oil pump is a pump that is driven by an electric motor.
The electric oil pump is able to supply the oil even in an engine stop state. Thus the electric oil pump is favorable for the oil supply to the transmission in a vehicle in which the so-called idling stop control that stops the engine when the vehicle stops is performed. Normally, the electric oil pump is provided in addition to the mechanical oil pump, then the oil supply is ensured using the engine-driven mechanical oil pump when the engine operates, and the oil supply is ensured using the electric oil pump when the engine stops.
Here, in a case of the electric oil pump, since the electric oil pump is driven by the electric motor, an oil discharge pressure from the oil pump depends on a pump drive torque of this electric motor. That is, in order to discharge the oil from the oil pump at a predetermined discharge pressure, the electric motor is controlled so as to output the pump drive torque according to this predetermined discharge pressure.
However, pressure of the oil discharged from the electric oil pump depends on viscosity of the oil. Further, the oil viscosity varies according to temperature of the oil. For this reason, for example, because the oil viscosity is high when the oil temperature is low, even if the electric motor drives the electric oil pump at the pump drive torque according to the predetermined discharge pressure, an actual discharge pressure does not reach the predetermined discharge pressure. In this case, in order to obtain the predetermined discharge pressure, it is required to increase the pump drive torque.
For this problem, Japanese Patent Provisional Publication No. 2006-161851 (hereinafter is referred to as “JP2006-161851”) discloses a hydraulic supply device that operates an electric motor by giving a command to the electric motor with a pump drive torque to be outputted being a torque command value. In JP2006-161851, temperature of oil (working fluid) is detected by an oil temperature sensor, then by determining the torque command value in accordance with the detected oil temperature, the predetermined discharge pressure can be obtained.